Electricity

What comes to mind when you hear the word Electricity?

Water boy Lightning Team work Ac/Dc Charge

Electricity in our lives. Two different types current: Alternating current (AC): i.e. Outlets

in walls

Direct Current (DC): i.e. Batteries, out the positive, in the negative.

Ohm’s Law Ohm’s Law: the current between two

points is directly proportional to the potential difference or voltage, and inversely proportional to the resistance.

∆V = IR∆V = Voltage/ Potential

difference -Volt (V)I = Current – Amp (A)R = Resistance –Ohm (Ω)

Voltage/Potential Difference.

the electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy. Refer to page 691 in text book.

Think of gravitational potential difference.∆E = mgh

V = ∆E/QV = Voltage/ Potential difference -Volt (V)∆E = change in electrical potential energy- Joule (J)Q = quantity of charge –Coulomb (C)

Voltage/Potential Difference cont.

Ex. A battery has a potential difference of 18.0 V. How much work is done when a charge of 64.0 C moves from the anode to the cathode?

V= 18.0 VQ = 64.0C V = ∆E/Q

∆E = VQ∆E = (18.0V)(64.0C)∆E = 1152J

Current Current: a flow of electric charge.

From positive to negative. The current can be calculated with

the following equation: I = Q/t

Q = quantity of charge transferred– Coulombs (C)

∆t = time interval that the charge is transferred – Seconds (s)

Example 1: A toaster runs for 2.5 minutes in which 9.60 A of current were required. Find the amount of charge that passed through the toaster.I = 9.60 A∆t = 2.5min = 150s I = Q/∆t

Q = I ∆tQ = (9.60A) (150s)Q = 1440 C

Current cont.

Resistance Resistance: is the hindrance to the

flow of charge. 3 main variables that contribute to

resistance.• the total length of the wires will affect the

amount of resistance. Longer the wire, more resistance.

• the wider the wire, the less resistance that there will be to the flow of electric charge

• the material that a wire is made of

Resistance cont. The conducting ability of a material is

often indicated by its resistivity. Lower the resistivity the better the conductor.

Kitchen appliances such as electric mixers and light dimmer switches operate by altering the current at the load by increasing or decreasing the resistance of the circuit.

Example 2. A 30 V battery maintains current through a 10 Ω resistance. What is the current?V = 30VR = 10Ω

∆V = IRI = V/RI = 30V/10ΩI = 3.0A

Resistance cont.

Ohm's Law as a Predictor of Current

The Ohm's law equation can be rearranged and expressed as:

I = ∆V/RThe current in a circuit is directly

proportional to the electric potential difference.(battery voltage)

The current is inversely proportional to the total resistance offered by the circuit. 

Ohm’s Law as a predictor of current cont.

With the formula: I = ∆V/RBattery Voltage Total Resistance

Current1.5V 3Ω 0.5A3.0V 3Ω 1.0A3.0V 6Ω 0.5A3.0V 12Ω

0.25A

PowerPower: is the rate at which electrical

energy is supplied to or consumed by a circuit. P = ∆E/tP = rate of change in potential energy – Watt (W) ∆E = change in electrical potential energy- Joule (J)∆t = time interval that the change occurs over – Seconds (s)

Power in Circuits.

To determine the power across a circuit, we must combine the following 3 equations.

P = ∆E/t ∆V = ∆E/Q I = Q/t P = (∆V)(Q)/t

P = (∆V)(I)

Power in Circuits cont. Ex. Determine the power of a saw that

draws 12 amps of current when plugged into a 120V outlet.

I = 12A∆V = 120V P = ∆VI

P = (120V)(12A)P = 1440W

Other formulas for calculating power:P = I2 • R P = V2 / R

Homework: Pg. 692 # 1, 2, 3 Pg. 696 # 4, 5, 6 Pg. 714 # 21, 22